This invention relates to vibration cancellation in reciprocating machinery, and more particularly to a vibration absorber for a free piston Stirling engine. A free piston Stirling engine is a sealed power unit containing a piston and a displacer within a closed vessel. The piston and displacer reciprocate out-of-phase in the vessel to circulate a working fluid through a closed loop from a compression space, through a cooler, regenerator, and a heater to an expansion space and then back through the same loop cyclically to subject a working fluid to a thermodynamic cycle approximating the theoretical Stirling cycle.
A simple and reliable form of free piston Stirling engine contains a single displacer and a single power piston. This form of engine presents the simplest control problems but is inherently unbalanced. That is, the reciprocating masses transmit an alternating force to the sealed vessel and this force must be absorbed by massive mounting structure or a sophisticated suspension arrangement. One such suspension arrangement is shown in U.S. application Ser. No. 153,839 entitled, "A Suspension and Vibration Oscillation System Incorporated Into the Mass Flow System for a Linear Reciprocating Machine" filed on May 27, 1980, by Peter Curwen, et. al now U.S. Pat. No. 4,360,087. This arrangement is extremely effective and produces a remarkable cancellation of force on the system so that the sinusoidal force exerted by the case is completely cancelled by the suspension system and the connection to the ground experiences an insignificant transmitting force, if any.
Although this system works well, it would be desirable to provide a system more particularly designed for a free piston Stirling engine which automatically compensates for changing frequency and/or stroke of the reciprocating members in the engine. Moreover, certain installations of the free piston Stirling engine may necessitate the elimination of all substantial vibration by the vessel itself.